A bipartisan coalition from the Senate Commerce, Science and Transportation Committee has been discussing pushing its own bill if the administration doesn't release something by the fall.

The Senate Environment and Public Works (EPW) Committee has also been gathering input with an eye on drafting an infrastructure plan this summer.

And several Republicans met at the White House last week to try to get the ball rolling there on the issue.

“If Donald Trump fails to demonstrate leadership, Congress is just going to have to grab the rope,” Sen. Richard Blumenthal (D-Conn.) told The Hill. “There’s already been discussions among us, both Republicans and Democrats, about coming together [on infrastructure.]”

“Time is not on our side,” he added.

The ramped up effort comes as it appears more and more likely that Trump’s infrastructure proposal, which was once labeled as a 100-day priority but has yet to be released, won’t see action in Congress until next year.

GOP leaders have already signaled that infrastructure must wait on the sidelines until they tackle tax reform, which is likely to be a heavy lift.

And the White House piled another legislative item onto lawmakers’ plates this week, with its release of a sweeping bill to overhaul immigration laws.

The addition of immigration legislation is further dimming hopes that the rebuilding plan will move on Capitol Hill this year.

White House press secretary Sarah Huckabee Sanders said Monday that Trump remains committed to working with Congress on an infrastructure package.

The president also defended his decision not to put a rebuilding proposal at the top of the agenda, telling The Wall Street Journal it would have been a “waste” because it’s a bipartisan issue.

“A lot of people said you should have started with taxes or you should have started with infrastructure,” Trump said, according to a transcript obtained by Politico. “Well, infrastructure, I’ll actually have bipartisan support, and I can use infrastructure to carry other things along. So I don’t want to waste it at the beginning.”

But members of Congress who were initially excited by Trump’s vow to upgrade U.S. roads, bridges, airports and other public works are growing impatient.

“He said he wanted to make it a priority when he first came into office, and here we are, now into August,” Sen. Gary Peters (D-Mich.) told The Hill. “So it’s very frustrating that nothing has come forward, because our caucus is united that we want to do something.”

The legislation, sponsored by five Democrats and four Republicans, would create a new infrastructure financing authority to help states and localities better collaborate with the private sector on rebuilding projects.

“I think our best bet right now is to work across the aisle in the Senate, regardless of what the White House does,” Klobuchar told The Hill. “This is going on now. People want to move.”

While some lawmakers, especially in the House, have been reluctant to get ahead of the administration, others have been in a rush to get something done on what they say is a time sensitive issue.

For one thing, infrastructure improvements can cost more the longer a project goes without a fix. And lawmakers have expressed concern about getting a bill done in time for construction season, which typically starts in the spring.

Members may also be eager to score a legislative victory that they can point to during the midterm elections, especially after the latest healthcare defeat in the Senate.

Blumenthal acknowledged that it would be unusual for Congress to move ahead with a massive infrastructure package without the president, though he said it might be necessary if they don’t see progress by “early fall.”

“It would be unprecedented for a program of this scale and scope to be bereft of presidential leadership,” he said.

But not everyone has given up hope on Trump’s ambitious rebuilding promise just yet.

A small group of Senate Republicans had a lunch meeting at the White House last week with DJ Gribbin and Reed Cordish, two of Trump’s policy aides.